One important system on a commercial aircraft is the galley plumbing system. Both potable and waste water must be stored, circulated, and collected on the aircraft via the plumbing system. On a commercial aircraft, potable water is used for multiple applications, including drinking water, beverages such as coffee and tea, and cooking (steam ovens, rice boilers etc.), and as a result must meet certain safety regulated requirements. That is, to ensure that it fit for human consumption, potable water available on an aircraft has to meet certain minimum health and safety standards. This is partially accomplished with aggressive filtering, which also improves the taste and smell, and removes impurities and harmful bacteria. The aircraft plumbing system encompasses all aspects of water usage on a galley, and includes its associated hardware and components as well as the other galley equipment, either consuming or producing water.
To meet the requirements of potable water, galley plumbing systems must pass design requirements specified by the aircraft manufacturers and proving tests to ensure that the potable, waste and foul water systems remain separated and that no cross contamination can occur. Also, when the aircraft shuts down after completion of a flight, or for longer periods of storage or maintenance, all of the systems must be capable of draining completely to evacuate all residual water so as to eliminate all retained water that could potentially become contaminated or breed bacteria. To this end, the plumbing system must be capable of gravitational draining, i.e., receiving air into the system to cause rapid displacement and removal of any trapped water.
It is common practice in the airlines for potable water that has passed through the water filter of the plumbing system to be regarded as waste water. However, recent changes in policy by aircraft manufacturers that are driven by the need to conserve water, has led to requirements that potable water only becomes waste water when it has entered the galley sink. In view of this, it is possible to reclaim potable water by draining all other water fed devices including water boilers, faucets, ovens, filters, etc. into the fresh water tanks. In addition, at the resumption of service, the potable water supply circuit must be capable of being filled automatically without manual assistance, and all sections that may potentially trap air must be capable of self-venting. When filling the potable water circuit, it is important to remember that pressures vary depending on the aircraft and design.
One challenge when designing aircraft plumbing systems on an aircraft is preventing backflow of waste water, which can contaminate the system and foul the drains and venting devices. Moreover, in severe cases foul air from the waste water can rise up and make things unpleasant for the passengers. Accordingly, a reliable and effective stop valve is essential to permit flow through the system, but prevent back flow of waste water.